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Acquisition Mode
Acquisition mode refers to how time stream data is captured from block by block data acquisition (trigger settings) and how the device responds after the data is acquired. It is often used for impact testing or recording transient events.
Triggering is often used for impact testing.
Accept/Reject mode lets you view the data before accepting it in to the averaged spectra.
CoCo separates the data processing into three stages: data conditioning, acquisition mode and signal analysis. Acquisition Mode controls how the continuous time stream data is captured for block-by-block processing. Acquisition Mode control is applied after data conditioning and before the signal analysis stage. If a CSA does not include a block capture function then Acquisition Mode will not be used.
Data processing is separated into three stages.Note: in the description below, sometimes when we say “capture a block of data”, it really means that multiple blocks of data are captured from their own time streams. These blocks are all accurately time-synchronized.
Acquisition Mode
Acquisition Mode defines how the device responds when a trigger event is detected and includes the following options.
Free Run displays block data acquired from the time stream as fast as possible or at the overlap rate by the user. Free Run is commonly used to analyze the random or irregular signals.
Continuous after Trigger waits until a trigger event is detected. After the first trigger event, averaging is reset and the system runs in Free Run mode.
Single Shot with Trigger waits until a trigger event is detected. After the trigger event, the spectral analysis, if there is any, will reset its average back to 1, and waiting for the next trigger. This mode is the best if you want to observe the time signal block by block at a certain trigger event.
Single Shot without Trigger waits until you press the Run button, then acquires one block of data and returns to the wait condition. This mode is the best if you simply want to observe a time signal block by block at an arbitrary time.
Auto-Arm Trigger waits until a trigger event is detected, then a block is acquired and the system returns to the wait condition. If another trigger event is then detected the new block of data will be acquired. This processes will continue indefinitely with no user interaction. Averaging is reset after each trigger event. This mode is the best for repetitive data capture and spectral analysis if you have confidence in the signal quality. Caution should be used because a desired captured block of data can be replaced by a new undesired block of data if an addition trigger event occurs. Use Manual-Arm Trigger to ensure that the last block is not automatically replaced by a new triggered signal.
Manual-Arm Trigger waits until a trigger event is detected, then a block is acquired and the system changes to a hold condition. After the data capture, you will be prompted with an Accept/Reject dialog box. If you accept the new data capture then the block will be included into the average and the system will return to the wait mode. If you reject the new data capture, the new block will be discarded and the system will return to the wait for trigger mode. This mode is the best for applications such as impact hammer testing where you may not have confidence in the signal quality of some of the data blocks.
Trigger Source
Trigger Source defines what signal is used to determine a trigger event. Any time stream that is set as trigger source candidate in the CSA can be selected as trigger source on the CoCo-80. If a signal is not identified as a trigger source candidate in the CSA file then the signal will not appear on the list. This feature is designed to simplify the user interface and optimize the CoCo-80 computation resources.
The candidates of Acquisition Mode selection and Trigger Source selection will be defined by the CSA editor. The CSA editor will assign some the data streams after the data conditioning as candidates of trigger sources. For example, in a CSA there are 8 channels, if you only select ch1 and ch2 time streams as candidates of trigger source and then this CSA will only show ch1 and ch2 on the trigger source selection menu.
You may also define time streams other than native channels as trigger source candidate. For example, if in the CSA an RMS measurement is derived from ch1, this RMS time stream can be used as a trigger source.
Trigger Condition
Trigger Condition defines when a trigger is detected based on the signal level and the slope. The four choices are:
1. Trigger Source > High Level (rising edge)
2. Trigger Source < Low Level (falling edge)
3. Low Level < Trigger Source < High Level (level trigger)
4. (Trigger Source > High Level) OR (Trigger Source < Low Level) (edge trigger)
There are two types of trigger detection, one is called edge detection; the second level detection. In the trigger conditions above, 1, 2 and 4 are edge detection and 3 the level detection. Edge detection compares at least two sample points against the threshold level. Level detection only detects one sample point.
When Free Run is selected, trigger source and level are not needed.
The table below visually explains when the trigger event will happen in these four conditions. The red mark shows the instant in time that the trigger event is detected:
Trigger Condition
Visual Explanation
Trigger Source > High Level (rising edge)
Trigger Source < Low Level (falling edge)
Low Level < Trigger Source < High Level (level trigger)
(Trigger Source > High Level) OR (Trigger Source < Low Level) (edge trigger)
Trigger Delay
Trigger delay allows a captured signal to include some data before or after the trigger event. This is done by defining some number of points, or the percentage of the total Block Size, that the capture occurs after the trigger event. For example, if the Block Size is set to 1024 and the trigger delay is 10%, the data capture will happen 102 points after the trigger event.
A negative trigger delay is more common for transient data capture. Negative trigger delay means that the data capture will include data points before the trigger event. For example, a -10% trigger delay means that the data capture will include 102 data points before the trigger event with Block Size 1024. Some instruments call a negative trigger delay a Pre-Trigger. The following picture shows the concept of a negative trigger delay:
Figure 60. Pre-Trigger (negative delay ) example.Overlap
When overlap is enabled, then the data is averaged from data frames that are overlapping. This reduces the averaging time. Overlap is only used when the Acquisition Mode is set to Free Run or Continuous after Trigger. Otherwise it is not used. Continuous capture without further trigger can also use overlapping.
No Overlap - Overlap is not applied.
Automatic - System determines the best overlap rate
25% Overlap - Frames are overlapped by 25%.
50% Overlap - Frames are overlapped by 50%.
75% Overlap - Frames are overlapped by 75%.
Using a Trigger During Measurement
This section explains the trigger operation while making measurements. Manual-Arm Triggering is the most common mode and will be described first and in the most detail. The other types will be explained briefly afterwards.
Manual Arm Trigger
When the Acquisition mode is setup then a small popup window is displayed as shown in Figure 61 indicating that the system is waiting for a trigger event. No signals are displayed until a trigger event is detected.
Waiting for trigger message.You can change from the waiting for trigger mode to Hold mode by pressing the F6 (Hold) button. The window will close and the system will change to Hold mode.
Press Restart (F3) or Run (F6) to reopen the window and return to the waiting for trigger mode.
When a trigger event occurs due to the Trigger Source signal meeting the trigger condition, the popup window will show a block of capture of data from the trigger source signal.
Trigger window with Accept or Reject options.The display will depend on the type of signals in the pane.
1. If a time stream is displayed then the display will update continuously. You will not notice the difference before or after trigger event for the time stream.
2. If a block signal is displayed, the block signal(s) in the background window will be updated with the new content.
3. If a block signal in the frequency domain is displayed, it will not be updated because you have not “accept” the time signal yet.
Now you may do one of two things: Accept or Reject.
If you press the Accept button, the acquired block signals will be passed to the signal analysis stage, usually windowing, FFT and spectral analysis. Then you can continue to the Next frame of capture.
After you press the Next key, the system will go back to waiting in trigger mode.
If you press Reject then the captured time signals will be discarded and will not be sent to signal analysis stage. After the Reject action, the system goes back to waiting in trigger mode.
The number showed on the top status bar, #N, indicates the number of the frames of the time captures that have been accepted and averaged into the spectra.
After you press the Hide key, the small from window will disappear. Press Enter to show this window again.
During trigger operation you can switch the main display window to any trace. This can be helpful to view the time stream selected as the trigger source to tune the level and slope settings.
